In some welding methods falling into this general category, the filler metal is supplied in the form of a wire which is unwound from a reel as fast as it is used up. In this type of method, the wire is sometimes used as an arc-formin electrode, and sometimes not.
For accurate welding, the end of the filler wire must be suitably guided relative to the zone to be welded. Further, the wire must be moved along a weld line smoothly and without jerking.
Traditionally, the wire of filler metal is guided by a tube having a bore with a rear opening through which the wire enters the tube and a front opening through which a short length of wire projects to be presented in a suitable position next to a weld zone.
In many methods, a welding machine further includes a nozzle for blowing an inert or an active gas over the weld zone to keep it under a controlled atmosphere. This avoids unwanted reactions of the molten material with the surrounding air or possibly with the gasses evolved by the welding operation.
In high performance welding machines, the position relative to the weld both of the gas nozzle and of the system for feeding filler wire to the weld zone are adjustable under the control of automatic regulator apparatus. Such apparatus is used in particular to maintain certain parameters of the welding operation, eg. the arc current, within set limits thereby optimising operating conditions.
There is increasing development of such welding apparatus in order to weld high performance parts whose quality must remain very high with excellent reliability. In particular they can be used to weld together parts made from materials that are usually difficult to work and which do not mix readily with other materials.
Nonetheless, such apparatus can be difficult to use. In particular, the front ends of the filler metal guide tubes tend to deteriorate rapidly and to suffer from all sorts of incidents in which the filler metal wire sticks to the guide tube. This results in rapid deterioration of the quality of a welding machine's welding, and its automatic regulation mechanisms cease to operate correctly. These difficulties lead to the guide tubes being replaced frequently, which is an expensive operation since it halts production and consumes a large number of guide tubes.
It has further been observed in installations that use inert gas blowing nozzles, that the nozzle itself tends to deteriorate causing the size of the gas outlet to vary, in particular to get smaller, thereby perturbing the flow of gas over the weld.
Finally, in those cases where the guide tube is also used to supply electricity to the filler metal wire, rapid deterioration has been observed in the quality of the electrical contact therebetween, leading to all sorts of incidents in the operation of the welding apparatus, and to rapid degradation in the quality of the welds obtained.
Attempts have already been made to improve the electric contact by providing the guide tubes, also known as contact tubes in this case, with means for taking up the play between the filler metal wire and the tube bore, so that there is always a push fit between them regardless of the amount of wear. However, the means used for this purpose up to now have never been as successful as expected. This stems either from the fact that the mechanism provided is too complex, or from the fact that the mechanisms do not stand up well to the very high operating temperatures of the contact tubes, or else from the fact that the mechanisms themselves give rise to parasitic electric arcs which tend to destroy them.
In the face of these difficulties, preferred embodiments of the present invention provide welding apparatus, and in particular components for the portions thereof which are in the immediate vicinity of the welding process, having greatly extended lifetimes compared with existing apparatus and/or components, and which substantially improve, at reasonable cost, the quality of the welds obtained by maintaining high degree of regularity over long operating periods using the same components.